Abstract

The use of organochlorine pesticides in rice growing in Laos is widespread. Potential contamination of pesticides to the aquatic organisms and sediments is a major concern. This study investigates the organochlorine pesticide contamination in fish, mollusks, and sediment from five main fishing areas of Vientiane, the capital of Laos. The fishing areas are located within the rice fields around Vientiane.
Fifteen species of freshwater fish and one species of mollusks were homogenized, extracted, fractionated and subsequently analysed with Gas Chromatography Mass Spectrometry (GC-MS). Sediment samples were extracted and fractionated and analysed similarly as those of fish and mollusks.
The target compounds of interest were lindane, chlordane, dieldrin, DDT and its derivatives. The result of this study shows that DDT, lindane, HCH, chlordane and dieldrin were present in 14 of 15 species of fish and mollusks. DDT, chlordane and dieldrin were present in the samples of sediment. This study also shows that lindane and chlordane has the highest concentrations both in fish and mollusk while DDT and its metabolites reveals next highest concentrations. Results show that highest concentrations of DDT, dieldrin and chlordane were observed in sediments.
Results from this study indicate that organochlorine contamination occurs in fish and mollusks. Laotian depends on fish and mollusks for their dietary needs of protein and this is a cause of major concern for potential human health impacts. Furthermore, sedimentary environments where the study were being conducted shows appearance of DDT, dieldrin and chlordane and this would increase the bio-availability of those compounds to the aquatic organisms including fish and mollusks.
Although, this study indicate that the levels of pesticides in fish, mollusk and sediment are below the World Health Organization (WHO) standards, the authority should try their best to reduce pesticide contamination in Vientiane, Laos. This study is the first of its kind in Laos and it provides important base-line information for policy makers and monitoring agencies.